1. Field of the Invention
The present disclosure generally relates to apparatus and methods for separating volatiles from particulates. More particularly, the present disclosure relates to apparatus and methods for separating volatile hydrocarbons from polymer particulates.
2. Description of the Related Art
In gas-phase polymerization, a gaseous stream containing one or more monomers is passed through a fluidized bed under reactive conditions in the presence of a catalyst. A polymer product is withdrawn from the reactor while fresh monomer is introduced to the reactor. Residual gaseous and/or liquid components such as unreacted hydrocarbon monomer(s) and/or diluent(s) are usually absorbed in the polymer product. These volatile, unreacted monomers and/or diluents need to be removed from the polymerized particulates. The polymer particulates are generally porous, unmelted, and range in size from about 0.1 mm to about 2.5 mm.
Typically the polymer product is introduced to a separator (often referred to as a purge bin) and contacted with a countercurrent flow of a purge gas such as nitrogen. Current purge bin designs, however, leave a substantial amount of unreacted monomer(s) and/or diluent(s) mixed with the polymerized particulates. Thus, current purge bin designs not only waste valuable monomers and/or diluents, but can lead to safety hazards because there is a danger of explosion if the concentration of the monomer(s) and/or diluent(s) becomes excessive in the presence of oxygen. Alternatively, larger purge bins are employed and/or the flow rate of purge gas is increased. Each of these approaches increases the cost and/or materials required for adequately purging the polymer product. There is a need, therefore, for improved apparatus and methods for separating volatile hydrocarbons from polymer particulates.